1. Field of the Invention
The invention relates to gearboxes used to drive rotating shafts and, more particularly, relates to an air-cooled gearbox assembly usable, e.g., to drive a rotor assembly of a concrete finishing trowel.
2. Description of the Related Art
Gearboxes are used to transfer torque to rotating shafts in a variety of environments in which the gearbox must be cooled to prevent it from overheating. One such application is a riding concrete finishing trowel. Riding finishing trowels can finish large sections of concrete more rapidly and efficiently than manually pushed finishing trowels. The typical machine of this type includes a mobile frame having a deck that supports an operator""s platform. At least two, and sometimes three or more, rotor assemblies are mounted on an underside of the deck. Each rotor assembly includes a driven shaft extending downwardly from the deck and a plurality of trowel blades. The trowel blades extend radially outwardly from the bottom end of the driven shaft and support the machine on the surface to be finished. In use, the weight of the finishing trowel and the operator is transmitted frictionally to the concrete by the rotating blades, thereby smoothing the concrete surface. The individual blades usually can be tilted relative to their supports to alter the pitch of the blades, and thereby to alter the pressure applied to the surface to be finished by the weight of the machine. In addition, the rotor assemblies are tiltable for steering purposes.
The driven shafts of the rotor assemblies are driven by one or more self-contained engines that are mounted on the frame and that are linked to the driven shafts by gearboxes. Each gearbox includes a housing tiltably mounted on the frame, an input shaft extending horizontally from the housing, and an output shaft extending vertically downwardly from the housing and coupled to the driven shaft of the rotor assembly. The input shaft is coupled to the output shaft by internal gears that are lubricated by a liquid lubricant.
The typical gearbox generates substantial heat during operation and must be cooled to prevent its lubricant from overheating and breaking down. Some gearboxes are air-cooled by a blower that is mounted on an end of the gearbox housing. The blower forces air laterally across the end of the housing without diverting the air over or under the gearbox. This airflow pattern results in relatively ineffective cooling because the most critical surfaces of the housing are not subjected to convective forced air heat transfer. The gearbox therefore must be oversized to prevent it from overheating. This oversizing requirement results in unnecessary weight and expense.
It is therefore a first principal object of the invention to provide an air-cooled gearbox assembly having an enhanced thermal capacity when compared to traditional air-cooled gearboxes.
Another object of the invention is to provide a gearbox assembly that meets the first principal object of the invention and that incorporates an improved cooling arrangement.
In accordance with a first aspect of the invention, these objects are achieved by providing an air-cooled gearbox assembly comprising a gearbox and an air cooler. The gearbox includes an input shaft, an output shaft, and a housing. The housing has upper and lower surfaces, an end wall which extends between the upper and lower surfaces, and inboard and outboard sidewalls which flank the end wall. The air cooler is configured to deflect air flowing along the end wall of the housing over at least one of the upper and lower surfaces of the housing. It comprises a blower and a plurality of spaced fins which are disposed on the end wall of the housing.
Preferably, the blower comprises an impeller and a shroud which houses the impeller and which overlies the fins. The shroud and the fins form airflow passages that extend between the fins to at least one of the upper and lower surfaces of the housing.
As a result of the increased thermal capacity achieved using this arrangement, a gearbox that weighs less than 50 lbs can be rated for a gearbox output speed of 200 rpm at an input speed of 4,000 rpm when driven by a 10-15 hp input.
Another principal object of the invention is to provide an improved method of cooling an air-cooled gearbox.
In accordance with another aspect of the invention, this object is achieved by forcing air at least generally horizontally across an end wall of a gearbox housing, and deflecting at least a substantial portion of the air at least generally vertically along the end wall and onto at least one of upper and lower surfaces of the housing, thereby cooling the at least one surface.
In order to prevent air from short-circuiting cooling passages of the gearbox assembly, measures are preferably taken for at least substantially preventing air from flowing past the sidewalls of the housing.
In addition, the deflecting step preferably comprises deflecting the air both upwardly and downwardly from a horizontal parting line on the end wall in order to effectively cool both the upper and lower surfaces of the gearbox.
These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.